1. Field of the Invention
The present invention relates to carbon nanotube displays (CNDPs), and in particular relates to an apparatus and method for calibrating the brightness of the CNDPs.
2. Description of the Related Art
A carbon nanotube display (CNDP) is a very popular field-emission display. With high brightness and wide viewing angles as cathode ray tube (CRT) displays and a small size and light weight as liquid crystal displays (LCD), demand for CNDPs is expected to continue to grow in the future.
FIG. 1 is a schematic diagram illustrating the driver circuit of the CNDP. The CNDP 100 comprises a plurality of pixels 102. The output stage 104 of the driver circuit 110 further comprises a p-type MOSFET (PMOS) 112 and an n-type MOSFET (NMOS) 114, and each of the transistors 112 and 114 comprises a gate coupled to a pixel signal Sp and controlled by the pixel signal Sp. When the voltage of the pixel signal Sp is low, the PMOS 112 is turned on and the NMOS 114 is turned off. Thus, the voltage of the pixel 102 rises to about the high voltage VH. Contrarily, when the voltage of the pixel signal Sp is high, the PMOS 112 is turned off and the NMOS 114 is turned on. Thus, the voltage of the pixel 102 falls to about the low voltage VGND. Therefore, the pixel 102 is driven by the pixel signal Sp.
FIG. 2 is a schematic diagram illustrating the transfer characteristic curve of the pixel 102 of the CNDP 100. In the initial stage of using the CNDP 100, the pixel 102 has a transfer characteristic curve 202 as shown in FIG. 2. However, owing to a special basic characteristic of the CNDP, the transfer characteristic curve 202 of the pixel 102 of the CNDP 100 is often shifted, wherein the transfer characteristic curve 204 is increased over time. In the prior art, the pixel 102 is applied by a constant current Iconst as shown in FIG. 2, and as time goes by, the voltage on the pixel 102 is shifted from voltage V1 to voltage V2. The shifting voltage causes the brightness of the CNDP 100 to accordingly increase, thus making the display quality of the CNDP unstable.
Therefore, an apparatus for calibrating the brightness of a CNDP is desired.